HiRes 2001( High Resolution Imaging in Small Animals with PET, MR and Other Modalities: Instrumentation, Applications and Animal Handling) will be the fourth in a series of successful, bi-annual international meetings focused on high-resolution in vivo imaging in biomedical research. This meeting brings together physicists, biomedical researchers, veterinarians, physicians and engineers working to develop new small animal imaging tools and methods, including research related to PET, MRI, SPECT, x-ray CT, ultrasound, optical imaging, EPR imaging and other modalities. The meeting will be held at the Double Tree Hotel and Executive Meeting Center in Rockville, Maryland from 9 September to 11 September 2001. We anticipate 250 attendees. The scientific program will be comprised of oral and poster presentations of solicited and invited papers. In addition to detector, data acquisition, and image analysis aspects of the various modalities, topics from application areas including molecular biology, the pharmaceutical industry, experimental applications, cross-modality imaging, data analysis, and other related areas will be considered. As part of the program, the National Cancer Institute and others will present special sessions on small animal handling techniques for various imaging modalities and on general approaches to animal preparation including blood sampling, physiologic monitoring, etc. The preliminary program, as well as details on registration and lodging may be found at the HiRes website: http://www.ornl.gov/HiRes2001.